Virus inactivation by sequential ultraviolet-chlorine disinfection: Synergistic effect and mechanism.

The COVID-19 outbreak has raised concerns about the efficacy of the disinfection process followed in water treatment plants in preventing the spread of viruses. Ultraviolet (UV) and chlorine multi-barrier disinfection processes are commonly used in water treatment plants; however, their effects on virus inactivation are still unclear. In this study, the effects of different disinfection processes (i.e., UV, free chlorine, and their combination) on waterborne viruses were analyzed using bacteriophage surrogates (i.e., MS2 and PR772) as alternative indicators. The results showed that the inactivation rates of PR772 by either UV or free chlorine disinfection were higher than those of MS2. PR772 was approximately 1.5 times more sensitive to UV disinfection and 8.4 times more sensitive to chlorine disinfection than MS2. Sequential UV-chlorine disinfection had a synergistic effect on virus inactivation, which was enhanced by an increase in the UV dose. As compared with single free chlorine disinfection, UV irradiation at 40 mJ cm-2 enhanced MS2 and PR772 inactivation significantly with a 2.7-fold (MS2) and a 1.7-fold (PR772) increase in the inactivation rate constants on subsequent chlorination in phosphate buffered saline. The synergistic effect was also observed in real wastewater samples, in which the MS2 inactivation rate increased 1.4-fold on subsequent chlorination following UV irradiation at 40 mJ cm-2. The mechanism of the synergistic effect of sequential UV-chlorine disinfection was determined via sodium dodecyl sulfate-polyacrylamide gel electrophoresis, using MS2 as an indicator. The results showed that the synergistic effect was due to damage to MS2 surface proteins caused by previous UV disinfection, which enhanced the sensitivity of MS2 to chlorination. This study provides a feasible approach for the efficient inactivation of viruses in water supply and drainage.

Effectiveness of Bacteriophage Therapy in Field Conditions and Possible Future Applications.

BACKGROUND: Bacteriophages are viruses, which are obligate parasites of specific bacteria for the completion of their lifecycle. Bacteriophages could be the possible alternative to antibioticresistant bacterial diseases. With this objective, extensive research in different fields is published which are discussed in this article. METHODS: After a review of bacteriophage therapy, bacteriophages were found to be effective against the multidrug-resistant bacteria individually or synergistically with antibiotics. They were found to be more effective, even better than the bacteria in the development of a vaccine. RESULTS: Apart from the bacteriophages, their cell contents like Lysin enzymes were found equally very much effective. Only the major challenge faced in phage therapy was the identification and characterization of bacteria-specific phages due to the wide genetic diversity of bacterial populations. Similarly, the threshold level of bacteriophages to act effectively was altered by ultraviolet radiation and heat exposure. CONCLUSION: Thus, bacteriophage therapy offers promising alternatives in the treatment of antibioticresistant bacteria in different fields. However, their effectiveness is determined by a triad of bacteriophages (type & quantity), host (bacteria) and environmental factors.

Biological properties and genomics analysis of vB_KpnS_GH-K3, a Klebsiella phage with a putative depolymerase-like protein.

Bacteriophages have been recently revisited as an alternative biocontrol tool due to the limitations of antibiotic treatment. In this study, we reported on the biological characteristics and genomic information of vB_KpnS_GH-K3 (abbreviated as GH-K3), a Klebsiella phage of the Siphoviridae family, which was previously isolated from a hospital sewage system. One-step growth curve analysis indicated that the burst size of GH-K3 was 291 PFU/cell. GH-K3 maintained a stable titer in a broad range of pH values (6-10) and temperature (up to 50 °C). Based on bioinformatics analysis, GH-K3 comprises of 49,427 bp containing a total of 77 open reading frames (ORFs), which share high degree of nucleotide similarity and close evolutionary relationships with at least 12 other Klebsiella phages. Of note, GH-K3 gp32 was identified as a unique ORF. The major segment of gp32 sequence at the C-terminus (residues 351-907) was found highly variable as determined by its mismatch with the nucleotide and protein sequences available at NCBI database. Furthermore, HHpred analysis indicated that GH-K3 gp32 contains three domains (PDB ID: 5W6S_A, 3GQ8_A and 1BHE_A) similar to depolymerase (depoKP36) of Klebsiella phage KP36 suggestive of a potential depolymerase activity during host receptor-binding in the processes of phage infection. Altogether, the current data revealed a novel putative depolymerase-like protein which is most likely to play an important role in phage-host interaction.

Ultraviolet inactivation of bacteria and model viruses in coconut water using a collimated beam system.

This study investigated the effect of ultraviolet-C irradiation on the inactivation of microorganisms in coconut water, a highly opaque liquid food (1.01 ± 0.018 absorption coefficient). Ultraviolet-C inactivation kinetics of two bacteriophages (MS2, T1UV) and three surrogate bacteria (Escherichia coli, Salmonella Typhimurium, Listeria monocytogenes) in 0.1% (w/v) peptone and coconut water were investigated. Ultraviolet-C irradiation at 254 nm was applied to stirred samples, using a collimated beam device. A series of known ultraviolet-C doses (0-40 mJ cm-2) were applied for ultraviolet-C treatment except for MS2 where higher doses were delivered (100 mJ cm-2). Inactivation levels of all organisms were proportional to ultraviolet-C dose. At the highest dose of 40 mJ cm-2, three surrogates of pathogenic bacteria were inactivated by more than 5-log10 (p < 0.05) in 0.1% (w/v) peptone and coconut water. Results showed that ultraviolet-C irradiation effectively inactivated bacteriophage and surrogate bacteria in highly opaque coconut water. The log reduction kinetics of microorganisms followed log-linear and exponential models with higher R2 (>0.95) and low root mean square error values. The D10 values of 3, 5.48, and 4.58 mJ cm-2 were obtained from the inactivation of E. coli, S. Typhimurium, and L. monocytogenes, respectively. Models for predicting log reduction as a function of ultraviolet-C irradiation dose were found to be significant (p < 0.05). Fluid optics were the key controlling parameters for efficient microbial inactivation. Therefore, the ultraviolet-C dose must be calculated not only from the incident ultraviolet-C intensity but must also consider the attenuation in the samples. The results from this study imply that adequate log reduction of vegetative cells and model viruses is achievable in coconut water and suggested significant potential for ultraviolet-C treatment of other liquid foods.

Pond walls: inclined planes to improve pathogen removal in pond systems for wastewater treatment?

Attenuation of sunlight in wastewater treatment ponds reduces the depth of the water exposed to disinfecting irradiances. Shallow pond depth with paddlewheel rotation increases exposure of pathogens to sunlight in high rate algal ponds. Generation of thin films, using pond walls as inclined planes, may increase inactivation of pathogens by increasing sunlight exposure. The performance of a laboratory based model system incorporating an inclined plane (IP) was evaluated. F-RNA bacteriophage, in tap water or wastewater, was exposed to sunlight only on the IP with the bulk water incubated in the dark. MS2 inactivation was significantly higher when the IP was present (P < 0.05) with a 63% increase observed. Prolonged exposure increased MS2 die-off irrespective of IP presence. Versatility of the IP was also demonstrated with faster inactivation observed in both optically clear tap water and wastewaters. IPs of different surface areas produced similar inactivation rates when operated at similar hydraulic loading rates regardless of slope length.

Temperature-dependent virus lifecycle choices may reveal and predict facets of the biology of opportunistic pathogenic bacteria.

Melioidosis, a serious illness caused by Burkholderia pseudomallei, results in up to 40% fatality in infected patients. The pathogen is found in tropical water and soil. Recent findings demonstrated that bacterial numbers can be regulated by a novel clade of phages that are abundant in soil and water. These phages differentially infect their bacterial hosts causing lysis at high temperatures and lysogeny at lower temperatures. Thus seasonal and daily temperature variations would cause switches in phage-bacteria interactions. We developed mathematical models using realistic parameters to explore the impact of phages on B. pseudomallei populations in the surface water of rice fields over time and under seasonally changing environmental conditions. Historical records were used to provide UV radiation levels and temperature for two Thailand provinces. The models predict seasonal variation of phage-free bacterial numbers correlates with the higher risk of melioidosis acquisition during the "warm and wet" season. We find that enrichment of the environment may lead to irregular large amplitude pulses of bacterial numbers that could significantly increase the probability of disease acquisition. Our results suggest that the phages may regulate B. pseudomallei populations throughout the seasons, and these data can potentially help improve the melioidosis prevention efforts in Southeast Asia.

Solar photocatalytic disinfection of E. coli and bacteriophages MS2, ΦX174 and PR772 using TiO2, ZnO and ruthenium based complexes in a continuous flow system.

The performance of photocatalytic treatment processes were assessed using different photocatalysts against E. coli and bacteriophages MS2, ΦX174 and PR772, in a recirculating continuous flow compound parabolic collector system under real sunlight conditions. Suspended TiO2 and ZnO nanoparticle powders and Tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate in solution were tested separately, as well as in combination, using E. coli. For a 3-log reduction of E. coli in distilled water, inactivation rates in terms of cumulative dose were in the order Ru(bpy)3Cl2>(TiO2 & Ru(bpy)3Cl2)>(ZnO & Ru(bpy)3Cl2)>ZnO>TiO2>photolysis. Reactivation of E. coli was observed following all trials despite the detection limit being reached, although the reactivated colonies were observed to be under stress and much slower growing when compared to original colonies. Treatment with Ru(bpy)3Cl2 was also compared against standard photolysis of bacteriophages MS2, ΦX174 and PR772 with the order of photolytic inactivation for a 3-log reduction in terms of cumulative UV-A dose being ΦX174>PR772>MS2. However, MS2 was found to be the most susceptible bacteriophage to treatment with Ru(bpy)3Cl2, with complete removal of the phage observed within the first 15min of exposure. Ru(bpy)3Cl2 also significantly improved inactivation rates for PR772 and ΦX174.

Application of low frequency pulsed ohmic heating for inactivation of foodborne pathogens and MS-2 phage in buffered peptone water and tomato juice.

The purpose of this study was to inactivate foodborne pathogens effectively by ohmic heating in buffered peptone water and tomato juice without causing electrode corrosion and quality degradation. Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes were used as representative foodborne pathogens and MS-2 phage was used as a norovirus surrogate. Buffered peptone water and tomato juice inoculated with pathogens were treated with pulsed ohmic heating at different frequencies (0.06-1 kHz). Propidium iodide uptake values of bacterial pathogens were significantly (p < 0.05) larger at 0.06-0.5 kHz than at 1 kHz, and sub-lethal injury of pathogenic bacteria was reduced by decreasing frequency. MS-2 phage was inactivated more effectively at low frequency, and was more sensitive to acidic conditions than pathogenic bacteria. Electrode corrosion and quality degradation of tomato juice were not observed regardless of frequency. This study suggests that low frequency pulsed ohmic heating is applicable to inactivate foodborne pathogens effectively without causing electrode corrosion and quality degradation in tomato juice.

Gene Expression Patterns during Light and Dark Infection of Prochlorococcus by Cyanophage.

Cyanophage infecting the marine cyanobacteria Prochlorococcus and Synechococcus require light and host photosystem activity for optimal reproduction. Many cyanophages encode multiple photosynthetic electron transport (PET) proteins, which are presumed to maintain electron flow and produce ATP and NADPH for nucleotide biosynthesis and phage genome replication. However, evidence suggests phage augment NADPH production via the pentose phosphate pathway (PPP), thus calling into question the need for NADPH production by PET. Genes implicated in cyclic PET have since been identified in cyanophage genomes. It remains an open question which mode of PET, cyclic or linear, predominates in infected cyanobacteria, and thus whether the balance is towards producing ATP or NADPH. We sequenced transcriptomes of a cyanophage (P-HM2) and its host (Prochlorococcus MED4) throughout infection in the light or in the dark, and analyzed these data in the context of phage replication and metabolite measurements. Infection was robust in the light, but phage were not produced in the dark. Host gene transcripts encoding high-light inducible proteins and two terminal oxidases (plastoquinol terminal oxidase and cytochrome c oxidase)-implicated in protecting the photosynthetic membrane from light stress-were the most enriched in light but not dark infection. Among the most diminished transcripts in both light and dark infection was ferredoxin-NADP+ reductase (FNR), which uses the electron acceptor NADP+ to generate NADPH in linear photosynthesis. The phage gene for CP12, which putatively inhibits the Calvin cycle enzyme that receives NADPH from FNR, was highly expressed in light infection. Therefore, both PET production of NADPH and its consumption by carbon fixation are putatively repressed during phage infection in light. Transcriptomic evidence is thus consistent with cyclic photophosphorylation using oxygen as the terminal electron acceptor as the dominant mode of PET under infection, with ATP from PET and NADPH from the PPP producing the energy and reducing equivalents for phage nucleotide biosynthesis and replication.

Application of ultraviolet light-emitting diodes (UV-LEDs) for water disinfection: A review.

Ultraviolet (UV) disinfection is an effective technology for the inactivation of pathogens in water and is of growing interest for industrial application. A new UV source - ultraviolet light-emitting diode (UV-LED) - has emerged in the past decade with a number of advantages compared to traditional UV mercury lamps. This promising alternative raises great interest in the research on application of UV-LEDs for water treatment. Studies on UV-LED water disinfection have increased during the past few years. This article presents a comprehensive review of recent studies on UV-LEDs with various wavelengths for the inactivation of different microorganisms. Many inconsistent and incomparable data were found from published studies, which underscores the importance of establishing a standard protocol for studying UV-LED inactivation of microorganisms. Different UV sensitivities to UV-LEDs and traditional UV lamps were observed in the literature for some microorganisms, which requires further investigation for a better understanding of microorganism response to UV-LEDs. The unique aspects of UV-LEDs improve inactivation effectiveness by applying LED special features, such as multiple wavelengths and pulsed illumination; however, more studies are needed to investigate the influencing factors and mechanisms. The special features of UV-LEDs offer the flexibility of novel reactor designs for a broad application of UV-LED reactors.

Inactivation of Escherichia coli O157:H7 using ultraviolet light-treated bacteriophages.

Escherichia coli O157:H7 causes serious foodborne infections warranting the development of effective control measures. One control option is to use bacteriophages (phages), which are regarded as safe to humans and an environmentally friendly alternative to chemical antimicrobials. One of the few remaining safety concerns is the potential for phages to facilitate genetic exchange between bacteria so resulting in undesirable mobilisation of genes. UV treatment of phages causes a rapid loss in their ability to replicate, while maintaining their antibacterial activity, and so the use of UV-treated phages could be an alternative to the use of viable phages. Data presented here show the inactivation of E. coli O157:H7 by UV-treated phages in milk and on the surface of raw and cooked meat. A minimum concentration of approximately 10(5) PFU cm(-2) (pre-UV treatment titre) of UV-treated phages was required before inactivation of E. coli O157:H7 on the surface of meat was measurable, and 1-2 log10 CFU cm(-2) reductions were typically obtained at concentrations of around 10(7) UV-treated phages cm(-2) (pre-UV treatment titre). Inactivation of E. coli O157:H7 by UV-treated phages was less than that for untreated phages. The production of UV-treated phages was not optimised and it is possible that better reductions in pathogen concentration could be achieved for the same input UV-treated phages concentrations.

Isolation and Characterization of the Lytic Cold-Active Bacteriophage MYSP06 from the Mingyong Glacier in China.

As unique ecological systems, glaciers are characterized by low temperatures and low nutrient levels, which allow them to be considered as "living fossils" for the purpose of researching the evolution of life and the environmental evolution of the earth. Glaciers are also natural microbial "reservoirs". In this work, a lytic cold-active bacteriophage designated MYSP06 was isolated from Janthinobacterium sp. MYB06 from the Mingyong Glacier in China, and its major characteristics were determined. Electron microscopy revealed that bacteriophage MYSP06 had an isometric head (74 nm) and a long tail (10 nm in width, 210 nm in length). It was classified as a Siphoviridae with an approximate genome size of 65­70 kb. A one-step growth curve revealed that the latent and burst periods were 95 and 65 min, respectively, with an average burst size of 16 bacteriophage particles per infected cell. The bacteriophage particles (100 %) adsorbed to the host cells within 10 min after infection. Moreover, the pH value and thermal stability of bacteriophage MYSP06 were also investigated. The maximum stability of the bacteriophage was observed at the optimal pH 7.0, and the bacteriophage became completely unstable at the extremely alkaline pH 11.0; however, it was comparatively stable at the acidic alkaline pH 6.0. As MYSP06 is a cold-active bacteriophage with a lower production temperature, its characterization and its relationship with its host Janthinobacterium sp. MYB06 deserve further study.

UV-Sensitivity of Shiga Toxin-Converting Bacteriophage Virions Φ24B, 933W, P22, P27 and P32.

Shiga toxin-converting bacteriophages (Stx phages) are present as prophages in Shiga toxin-producing Escherichia coli (STEC) strains. Theses phages can be transmitted to previously non-pathogenic E. coli cells making them potential producers of Shiga toxins, as they bear genes for these toxins in their genomes. Therefore, sensitivity of Stx phage virions to various conditions is important in both natural processes of spreading of these viruses and potential prophylactic control of appearance of novel pathogenic E. coli strains. In this report we provide evidence that virions of Stx phages are significantly more sensitive to UV irradiation than bacteriophage λ. Following UV irradiation of Stx virions at the dose of 50 J/m², their infectivity dropped by 1-3 log10, depending on the kind of phage. Under these conditions, a considerable release of phage DNA from virions was observed, and electron microscopy analyses indicated a large proportion of partially damaged virions. Infection of E. coli cells with UV-irradiated Stx phages resulted in significantly decreased levels of expression of N and cro genes, crucial for lytic development. We conclude that inactivation of Stx virions caused by relatively low dose of UV light is due to damage of capsids that prevents effective infection of the host cells.

Photoreactivation of bacteriophages after UV disinfection: role of genome structure and impacts of UV source.

The UV inactivation kinetics of bacteriophages MS2, PhiX174, T1 and PRD1 and the potential of bacterial UV repair mechanisms to reactivate these bacteriophages is described here. The selected bacteriophages represent a range of genome size, single and double stranded genomes, circular and linear organization and RNA and DNA. Bacteriophages were exposed to UV irradiation from two different collimated beam UV irradiation sources (medium-pressure (MP) mercury lamps and low-pressure (LP) mercury lamps) and assayed during which host-phage cultures were exposed to photoreactivating light for 6 h, then incubated overnight at 37 °C in the dark. Dark controls following UV exposure were performed in parallel. UV inactivation kinetics (using dark controls) showed that circular ssDNA phage (PhiX174) was the most sensitive and linear ssRNA phage (MS2) was the more resistant phage. No photoreactivation was observed for MS2 (RNA phage) and the highest photoreactivation was observed for PRD1. In the case of PRD1, the dose required for 4-log reduction (dark control) was around 35 mJ/cm(2), with a similar dose observed for both UV sources (MP and LP). When the photoreactivation step was added, the dose required for 4-log reduction using LP lamps was 103 mJ/cm(2) and for MP lamps was 60 mJ/cm(2). Genome organization differences between bacteriophages play an important role in resistance to UV inactivation and potential photoreactivation mediated by bacterial host mechanisms. The use of photoreactivation during the assay of PRD1 creates a more conservative surrogate for potential use in UV challenge testing.

Analysis of actively transcribed DNA repair using a transfection-based system.

Host cell reactivation (HCR) is a transfection-based assay in which intact cells repair damage localized to exogenous DNA. This chapter provides instructions for the application of this technique, using as an exemplar UV irradiation as a source of damage to a luciferase reporter plasmid. Through measurement of the activity of a successfully transcribed and translated reporter enzyme, the amount of damaged plasmid that a cell can "reactivate" or repair and express can be quantitated. Different DNA repair pathways can be analyzed by this technique by damaging the reporter plasmid in different ways. Since it involves repair of a transcriptionally active gene, when applied to UV damage the HCR assay measures the capacity of the host cells to perform transcription-coupled repair, a subset of the overall nucleotide excision repair pathway that specifically targets transcribed gene sequences.

Inactivation of bacteriophage infecting Bacteroides strain GB124 using UV-B radiation.

Ultraviolet-B radiation (280-320 nm) has long been associated with the inactivation of microorganisms in the natural environment. Determination of the environmental inactivation kinetics of specific indicator organisms [used as tools in the field of microbial source tracking (MST)] is fundamental to their successful deployment, particularly in geographic regions subject to high levels of solar radiation. Phage infecting Bacteroides fragilis host strain GB124 (B124 phage) have been demonstrated to be highly specific indicators of human fecal contamination, but to date, little is known about their susceptibility to UV-B radiation. Therefore, B124 phage (n = 7) isolated from municipal wastewater effluent, were irradiated in a controlled laboratory environment using UV-B collimated beam experiments. All B124 phage suspensions possessed highly similar first order log-linear inactivation profiles and the mean fluence required to inactivate phage by 4 - log(10) was 320 mJ cm(-2). These findings suggest that phage infecting GB124 are likely to be inactivated when exposed to the levels of UV-B solar radiation experienced in a variety of environmental settings. As such, this may limit the utility of such methods for determining more remote inputs of fecal contamination in areas subject to high levels of solar radiation.

Norovirus and MS2 inactivation kinetics of UV-A and UV-B with and without TiO2.

Germicidal ultraviolet, such as 254-nm UV-C, is a common method of disinfection of pathogenic enteric viruses. However, the disinfection efficacies of UV-A or -B in terms of inactivating waterborne viruses such as norovirus have not been characterized. We evaluated the inactivation kinetics of MS2 bacteriophage and murine norovirus (MNV), a surrogate of human norovirus (NoV), by UV-A and -B. In addition to UV disinfection, we further investigated whether the presence of TiO2 could enhance the virus inactivation kinetics of UV-A and -B. Both MS2 and MNV were highly resistant to UV-A. However, the addition of TiO2 enhanced the efficacy of UV-A for inactivating these viruses. UV-A dose of 1379 mJ/cm(2) resulted in a 4 log10 reduction. In comparison, UV-B alone effectively inactivated both MS2 and MNV, as evidenced by the 4 log10 reduction by 367 mJ/cm(2) of UV-B. The addition of TiO2 increased the inactivation of MS2; however, it did not significantly increase the efficacy of UV-B disinfection for inactivating MNV. When these treatments were applied to field water such as groundwater, the results were generally consistent with the laboratory findings. Our results clearly indicated that UV-B is useful for the disinfection of waterborne norovirus. However, MNV was quite resistant to UV-A, and UV-A effectively inactivated the tested viruses only when used in combination with TiO2.

Effect of gamma irradiation on bacteriophages used as viral indicators.

This study aimed to examine the susceptibility of indicator bacteriophages towards γ-radiation to evaluate their appropriateness as viral indicators for water quality control. The effects of γ-radiation on naturally occurring somatic coliphages, F-specific coliphages and Escherichia coli were examined in raw sewage and sewage sludge. As well, the effects of radiation on bacteriophages ΦX174 and MS2, and E. coli all grown in the laboratory and seeded in distilled water, autoclaved raw sewage and a 1% peptone solution were evaluated. The inactivation of E. coli was fairly similar in all matrices. In contrast, inactivation of bacteriophages was significantly greater in distilled water than in the other matrices. These results showed the great influence of the matrix characteristics on virus inactivation. Somatic coliphages in raw sewage and sewage sludge and ΦX174 in autoclaved sewage were inactivated similarly and were far more resistant than F-specific coliphages, MS2 and E. coli. As well, F-specific RNA bacteriophages in raw sewage and sewage sludge and MS2 in autoclaved sewage were inactivated similarly and were more resistant than E. coli. In contrast, MS2 was more susceptible to γ-radiation than E. coli in distilled water. Our results showed that ΦX174 is a suitable indicator for estimating virus inactivation by γ-irradiation and corroborate the use of somatic coliphages to survey the viral quality of treated water and sludges.

Comparative analysis of the biological and physical properties of Enterococcus faecalis bacteriophage vB_EfaS_GEC-EfS_3 and Streptococcus mitis bacteriophage vB_SmM_GEC-SmitisM_2.

Enterococcus faecalis and Streptococcus mitis are common commensal inhabitants of the human gastrointestinal and genitourinary tracts. However, both species can be opportunistic pathogens and cause disease in nosocomial settings. These infections can be difficult to treat because of the frequency of antibiotic resistance among these strains. Bacteriophages are often suggested as an alternative therapeutic agent against these infections. In this study, E. faecalis and S. mitis strains were isolated from female patients with urinary tract infections. Bacteriophages active against these strains were isolated from sewage water from the Mtkvari River. Two phages, designated vB_EfaS_GEC-EfS_3 (Syphoviridae) and vB_SmM_GEC-SmitisM_2 (Myoviridae), were specific for E. faecalis and S. mitis, respectively. Each phage's growth patterns and adsorption rates were quantified. Sensitivity to ultraviolet light and temperature was determined, as was host range and serology. The S. mitis bacteriophage was found to be more resistant to ultraviolet light and exposure to high temperatures than the E. faecalis bacteriophage, despite having a much greater rate of replication. While each phage was able to infect a broad range of strains of the same species as the host species from which they were isolated, they were unable to infect other host species tested.

Susceptibility of non-enveloped DNA- and RNA-type viruses to photodynamic inactivation.

The comparative susceptibility of DNA- and RNA-type viruses to photodynamic inactivation has not yet been clearly addressed. In this study the effect of the tricationic porphyrin Tri-Py(+)-Me-PF on the inactivation of four DNA and three RNA non-enveloped phages was compared. The results obtained show that the photodynamic efficiency varied with the phage type, the RNA-type phages being much more easily photoinactivated than the DNA-type ones.